1. Field of the Invention
The present invention relates to methods and apparatus for replacing or supplementing the natural nucleus pulposus of an intervertebral disc by using a viscoelastic low-modulus implant through a transosseus approach, and more particularly to methods and apparatus for pressurizing a viscoelastic implant within the intervertebral disc to achieve an appropriate physiologic state of annulus tension and nucleus pressurization.
2. Brief Description of the Prior Art
Chronic back pain, typically lower back pain, is experienced by many individuals, and is responsible for much lost time at work and expense for treatment. Such pain is generally the result of a pathological condition of an intervertebral disc, caused by injury or age-related degeneration.
Current treatment options for lower back pain range from conservative bed rest to highly invasive surgical procedures including spinal fusion and discectomy. Spinal fusion, i.e., fusion or immobilization of the vertebrae on each side of the afflicted intervertebral disc, is a procedure that offers pain relief and an increased stability of the fused segment. Discectomy, i.e., surgical removal of part of the intervertebral disc is another surgical option.
Total disc replacement with a mechanical prosthesis has been proposed as another option for relief of back pain, and a number of such mechanical prosthesis have been proposed.
The human intervertebral disc is comprised of two major structures, an inner gelatinous nucleus pulposus and an outer tendinous structure, the annulus fibrosis. Degeneration of the nucleus leads to degradation and loss of function of the intervertebral disc, resulting in pain and disability. Consequently, another surgical option for the relief of lower back pain is replacement of the nucleus, leaving the annulus intact. Thus, the aim of nucleus replacement is to relieve pain, to restore healthy physiologic function to the disc, and to prevent additional wear on the annulus.
Normal disc function requires the combined action of the nucleus pulposus and annulus fibrosus. Consequently, a nucleus implant should preferably tend to restore the normal mobility of the disc, restore the disc height and re-create healthy disc pressure in order to place the annulus fibers back into their natural state of tension.
Accordingly, a need exists for a nucleus replacement device and a method of implantation that substantially reproduces the synergistic interaction between the nucleus and annulus, thus restoring the normal mechanical properties and mobility of the disc.